<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>scss方式改变主题</title>
</head>
<body>
  <div class="card">
    <h2 class="title">卡片标题</h2>
    <p class="content">卡片内容卡片内容卡片内容卡片内容卡片内容卡片内容卡片内容卡片内容卡片内容卡片内容</p>
  </div>
  <button id="change-btn">亮暗切换</button>
</body>
</html>